Plant pathogenic Ralstonia share two core methyl-accepting chemoreceptors that drive chemotaxis toward distinct amino acid profiles
Ralstonia solanacearum species complex pathogens cause bacterial wilt disease in diverse plant families. These pathogens use chemotaxis and motility to discover host roots. The specificity of this process is conferred by methyl-accepting chemotaxis proteins (MCPs). We explored pangenomic variation of MCPs and other chemotaxis machinery across Ralstonia wilt pathogens. We classified 19 MCPs as broadly conserved, core MCPs, and we identified several accessory MCPs. Within their periplasmic sensing domains, two of the core MCPs contain a motif that is known to bind amino acid ligands: McpA1 and McpA2. To identify the ligands of McpA1 and McpA2, we constructed HyChemosensor strains. In HyChemosensor strains, the periplasmic sensing domains of the MCPs were translationally fused to the signaling domain of a model two component sensor, NarQ. The HyChemosensor assays revealed that the receptors, McpA1 and McpA2, have overlapping binding profiles for acidic amino acids. Nevertheless, McpA2 recognized a broader profile of amino acids. Quantitative swim plate assays confirmed that these receptors facilitate Ralstonias chemoattraction to amino acids. Consistent with prior evidence in a different Ralstonia strain background, mcpA1 was dispensable for virulence on tomato. However, single or double mutants lacking mcpA2 demonstrated reduced virulence on tomato following naturalistic soil soak inoculations. Thus, McpA1 and McpA2 have distinct roles in plant colonization, despite redundancy in their chemical specificity.